Swivel chair support construction



Dec. 15, 1964 A. ANDERSON 3,161,396

SWIVEL CHAIR SUPPORT CONSTRUCTION Filed Sept. 5, 1963 2 Sheets-Sheet 1 Dec. 15, 1964 G. A. ANDERSON 3,

SWIVEL CHAIR SUPPORT CONSTRUCTION Filed Sept. 5, 1965 2 Sheets-Sheet 2 United Statesv Patent 3,1613% SWIVEL CHAR SUPPORT CONSTRUCTION George Albert Anderson, Gardner, Mass, assignor to Collier-Keyworth Company, Gardner, Mass, 21 corporation of Massachusetts Filed Sept. 5, 1963, Ser. No. 306,340 8 Claims. (6!. 248-405) This invention relates to a swivel chair support construction of the threaded spindle type and pertains more specifically to an improved construction having a selflocking feature to lock the chair at the desired height.

Swivel chair supporting constructions of the threaded spindle type are conventionally supplied to chair manufacturers with a fitting secured to the upper end of the spindle which is adapted to be fastened to the bottom of a chair seat. The fitting may in some cases incorporate a tilting mechanism which will make it possible to tilt the chair seat after the chair has been completed. The chair manufacturers stock a variety of seats and leg assemblies which may be combined with the swivel chair support construction. One of the parts of the support construction which must be varied to adapt it to a particular seat and leg assembly is the seat height adjustment handwheel or so-called bell which should properly be matched to the size and appearance of the leg assembly.

Inasmuch as the bell is used in adjusting the height of the chair seat, it must be engaged with the threads on the spindle; but it is also important that the lower part of the spindle be unthreaded if possible so as to provide a smooth, cylindrical bearing surface of large area in order to minimize wear. A conventional bell cannot be removed from a spindle having an unthreaded lower portion when the upper end of the spindle is permanently secured, as by staking, to the housing of the seat'fitting, so that the chair manufacturer must carry a large inventory of chair support constructions embodying a wide variety of hell sizes and shapes.

One object is to provide a swivel chair supporting construction of the type described having a threaded spindle with a smooth, cylindrical bearing surface at its lower end and on the threads of which any desired hell can readily be mounted by the chair manufacturer without the necessity for using any special tools or machinery.

Another object is to provide a swivel chair support construction of the type described embodying a self-locking feature which automatically locks the chair seat at the desired height when the weight of a person is in the chair seat while at the same time permitting the height of the chair to be readily adjusted by rotation of the bell when the chair is empty.

Still another object is to provide a novel split-nut connection between the bell and the threads of the spindle which not only facilitates assembly of the bell with the spindle, but which in addition provides a self-locking feature.

Other and further objects will be apparent from the drawing and from the description which follows.

In the drawings:

FIG. 1 is a view in side elevation, partly broken away and in section, showing one embodiment of the swivel chair support construction of the present invention;

FIG. 2 is a view taken along line 2-2 of FIG. 1;

FIG. 3 is a view on an enlarged scale in elevation, partly broken away and in section, showing details of the split-nut construction;

FIG. 4 is a view taken along line 4-4 of FIG. 3;

FIG. 5 is a view taken along lines-5 of FIG. 3;

FIG. 6 is a view taken along line 6-6 of FIG. 3;

FIG. 7 is a view in section, partly broken away, on a greatly enlarged scale, showing the interrelationship of the threads of the spindle and of the split-nut; and

FIG. 8 is an exploded view showing the relationship of the several parts at an intermediate stage of assembly.

Referring specifically to the drawings, the swivel chair support construction of the present invention includes a threaded spindle 10 having at its lower end a smooth, cylindrical bearing surface 12 free from threads. The upper end of the spindle is secured in any suitable manner, preferably by non-detachable staking, to a fitting 14 which is adapted to be secured to the bottom of a chair seat. Fitting 14 may be either of the tilting or nontilting variety. The leg assembly 16, which may be of any desired conventional construction, is provided with a bearing for supporting the spindle which in turn supports the chair seat. The bearing includes a washer 18 rigidly fastened to and seated on the top of the leg assembly and a flanged steel support collar 20 which is rigidly fastened, as by welding, to washer 18 and held in place by a swaged steel tube 22. Mounted within tube 22 is a bearing liner 24 of synthetic plastic composition supported on collar 20 by means of radially extending flange 26 which is formed integrally with liner 24. While a variety of materials such as synthetic plastic compositions are suitable for use in making the bearing liner, as is well known, the material preferred for best results is a superpolyamide. While the length of the lower unthreaded portion of spindle 10 is not critical, it is preferred that it beat least half the length of bearing liner 24.

Engaged with the threads of spindle 10 is a nut which is split or divided axially into two parts 30, 32. Each part carries a female thread which engages with the male thread of spindle 10 along approximately one half its periphery, the split extending diametrically across the tapped opening in the nut. The lines of juncture between the two parts 30, 32 of the nut are relieved adjacent both the top and the bottom of the nut to provide a pair of fulcrum points 34, 34 about which the parts may rock with respect to each other. Adjacent the upper margin of parts 30, 32 is a channel 36 (see FIG. 8) in which the periphery of a center opening through bell 38 is adapted to be seated. The bell 38 may be of any conventional size or shape to match the leg assembly 16. A cam is provided in the form of a metal cup 40 embracing the bottom portion of nut parts 30, 32 and having an aperture in its bottom through which spindle 10 extends. Cam cup 40 rests upon the upper surface of bearing liner 26 which forms a thrust bearing for it. As best appears in FIG. 3, the radius of curvature of the inside of cam cup 40 at the junction of the side and the bottom is greater than the radius of curvature of the corresponding portion of parts 30, 32 so that the bottom portions of the two parts are urged toward each other as they are forced toward the botom of cam cup 40. At the same time the upper portions are restrained from moving away from each other by engagement with the inner margin of bell 38.

The two parts 30, 32 of the split nut are preferably molded of a suitable resilient and tough synthetic plastic composition, such as a superpolyamide, which has good elastic memory and which does not appreciably absorb moisture, although other materials can be used. In order to prevent accidental separation of the assembly from the legs 16 when the chair is lifted, a spring detent 42 is preferably molded in the wall of each part 30, 32 and is positioned so as to engage an aperture 44 in the wall of cam cup 40 when the two parts have been inserted in the cup. In addition, a locking screw 46 extends inwardly from bell 38 to a position between washer 18 and the flange of collar 20, as best appears in FIG. 1, to prevent separation of the leg assembly 16 from the spindle and the bell and split-nut threaded on it. p

In order to minimize the possibility of cocking of the two parts 36, 32 and consequent possible binding of the nut parts on the spindle threads, it is desirable to provide a projecting lug 48 in the channel 36 of each part 36, 32. Each lug 48 registers with a corresponding aperture or cut-out in the margin of the central opening of bell 38, as shown in FIG. 2. It is also desirable that the depth of the threads in parts 30, 32 be reduced adjacent each margin, as shown at 50 in FIG. 6 in order to facilitate assembly of the split-nut in threaded engagement with the spindle.

In order to ensure positive locking of the nut parts to the threaded spindle, it is desirable that the included solid angle of the male threads 60 of the spindle, as seen in FIG. 7, measured in the plane of the spindle axis, be greater than the included angle of the female threads 62 of the nut .parts measured in the same plane. As a consequence of this interrelationship, the two sets of threads tend to wedge against each other when they are forced together by the action of cam cup 40 in urging the lower portions of the two split-nut parts 30, 32 toward each other.

The effectiveness of the locking action depends in part upon the location of fulcrum points 34, 34 with respect to the top and bottom of split-nut parts 30, 32. For best results the ratio of the distance between the top of the nut parts and the fulcrum points to the distance between the fulcrum points and the bottom of the nut parts should be from 1:7 to 1:13. In addition, the distance between the fulcrum points and the bottom, i.e. cam engaging portion, of the split-nut parts should be equal to at least one half and not more than twice the overall diameter of the threaded portion of the spindle. Such a construction provides locking of the chair height both when the chair is empty and when it is occupied. When empty, however, the split-nut parts may be rotated manually with respect to the spindle by means of bell 38 to vary the height of the chair.

In assembling the construction of the present invention, there is selected the desired chair seat having attached to its bottom the fitting 14 to which spindle has been staked. There is also selected the desired leg assembly 16 to which the desired bearing assembly 18, 20, 22, 24, 26 has been previously attached and a bell 38 of the proper size and shape to match the leg assembly 16 is selected. The end 12 of the spindle is then inserted through the central aperture of the bell 38 and the two split-nut parts 30, 32 are assembled on the threaded portion of the spindle beneath the bell with their upper portions inclined toward each other, as shown in FIG. 8. The bell is then moved into position to engage the channel 36 of the two split-nut parts, and the parts are pivoted about their fulcrum points 34 until channel 36 engages the margin of the hole in the bell with the projections 48 properly seated in the mating apertures of the bell. Cam cup 40 is then slipped over the end 12 of spindle 19 and pressed over the bottom portions of the split-nut parts 30, 32 until the detents 42 engage in the openings 44. The lower end 12 of the spindle 10 is then inserted in the bearing of the leg assembly 16 and locking screw 46 is put in place so that its inner end is in the position shown in'FIG. 1.

When thus assembled, the bottom of cam cup 40pmvides a thrust bearing surface resting on the top of bearing liner 26. The weight of the chair seat itself, which isusually at least pounds, is sufficient to lock the splitnut parts '30, 32 to the threads of spindle 10, even when the chair is not in use, so that accidental rotation of the chair seat with respect to the leg assembly will not change the height of the chair. Because of the low friction characteristics of bearing liner 26, the friction between the bottom of cam-cup 40 and friction'liner 26 is insufficient to effect rotation of the nut parts and the bell with respect to the spindle. The height can readily be adjusted, however, by manually rotating bell 38 with respect to the spindle 10, only a moderate amount of force being required to effect this rotation which carries with it the two nut parts 30, 32. When the desired position has been reached, the chair is again automatically locked in its new position. The addition of any weight to the chair seat, as for example the occupation of the chair by a person, simply serves to force the two nut parts more deeply into the cam cup 40 and press them more firmly into engagement with the threads of spindle 10, thus locking the assembly together even more tightly.

Although specific embodiments of the invention have been described herein, it is not intended to limit the invention solely thereto, but to include all of the obvious variations and modifications within the spirit and scope of the appended claims.

What is claimed is:

1. A swivel chair support construction comprising a spindle having one end adapted to be attached to a chair seat, a portion of said spindle being threaded for a sufficient distance to provide vertical adjustability of position of the chair to the desired extent, a nut engageable with the threaded portion of said spindle, said nut being divided axially into a plurality of separate parts to permit assembly thereof about and in threaded relation with the threaded portion of the spindle, and a cam engageable with said nut parts and adapted to be supported by a bearing for rotation about the axis of said spindle, said cam being arranged to hold said nut parts in rotatable threaded engagement with said spindle and to urge said nut parts into locking engagement with said spindle in response to the weight of said chair seat and its contents.

2. A swivel chair support construction as claimed in claim 1 in which the portion of the spindle remote from the chair seat has a smooth cylindrical bearing surface.

3. A swivel chair support construction as claimed in claim 1 in which the nut is a two-part nut split diametrically of its tapped opening and in which the lines of juncture between said parts are relieved adjacent both the top and the bottom of the nut to provide a pair of fulcrum points about which said parts may rock with respect to each other and in which means is provided to positively limit the outward rocking movement of the top of said parts about said fulcrum points and to rotate said parts on said threaded spindle and in which said cam acts to rock the bottom of said parts toward each other and to urge them into locked relation with said threaded spindle.

4. A swivel chair support construction as claimed in claim 3 in which the cam is in the form of a cup embracing at least the bottom portion of said nut parts and having an aperture in its bottom for the passage of the spindle therethrough.

5. A swivel chair support construction as claimed in claim 4 in which said nut parts are composed of a resilient synthetic plastic composition and the included solid angle of the male threads of the spindle, measured in the plane of the spindle axis, is greater than the included angle of the female threads of the nut measured in the same plane.

6. A swivel chair support construction as claimed in claim 4 in which said nut parts are composed of a resilient synthetic plastic composition and the ratio of the distance between the top of said parts and the fulcrum points to the distance between the fulcrum points and the bottom of said parts is from 157 to 1:13 and the last said distance is equal to at least one half the diameter of the threaded portion of the spindle.

7. A swivel chair support construction as claimed in claim 2 in which the cam is in the form of a cup embracing at least the bottom portion of said not parts having an aperture in its bottom for the passage of the spindle therethrough, said nut parts are composed of a resilient synthetic plastic composition, the ratio of the distance between the top of said parts and the fulcrum points to the distance between the fulcrum points and the bottom of said parts is from 1:7 to 1: 13 and the last said distance is equal to at least one half the diameter of the threaded portion of the spindle, and the included solid angle of the male threads of the spindle, measured in the plane of the spindle axis, is greater than the included angle of the female threads of the nut measured in the same plane.

8. A swivel chair support construction as claimed in claim 1 in which the nut parts are composed of a resilient synthetic plastic composition.

References Cited by the Examiner UNITED STATES PATENTS 8/90 Trapp 248-406 10 1'0/ 95 Morgan 248406 11/97 Sheriffs et al 248406 1/00 Starrett 85-33 Peters et a1. 248380 Collier et a1 248405 Bolens 248406 Harting 248406 Richards 108-136 McKinley 248-l88.7 Skeisvoll 8533 Moore 248161 Musser 74424.8 Ericson et al. 248405 Lie 248161 CLAUDE A. LE ROY, Primary Examiner. 

1. A SWIVEL CHAIR SUPPORT CONSTRUCTION COMPRISING A SPINDLE HAVING ONE END ADAPTED TO BE ATTACHED TO A CHAIR SEAT, A PORTION OF SAID SPINDLE BEING THREADED FOR A SUFFICIENT DISTANCE TO PROVIDE VERTICAL ADJUSTABILITY OF POSITION OF THE CHAIR TO THE DESIRED EXTENT, A NUT ENGAGEABLE WITH THE THREADED PORTION OF SAID SPINDLE, SAID NUT BEING DIVIDED AXIALLY INTO A PLURALITY OF SEPARATE PARTS TO PERMIT ASSEMBLY THEREOF ABOUT AND IN THREADED RELATION WITH THE THREADED PORTION OF THE SPINDLE, AND A CAM ENGAGEABLE WITH SAID NUT PARTS AND ADAPTED TO BE SUPPORTED BY A BEARING FOR ROTATION ABOUT THE AXIS OF SAID SPINDLE, SAID CAM BEING ARRANGED TO HOLD SAID NUT PARTS IN ROTATABLE THREADED ENGAGEMENT WITH SAID SPINDLE AND TO URGE SAID NUT PARTS INTO LOCKING ENGAGEMENT WITH SAID SPINDLE IN RESPONSE TO THE WEIGHT OF SAID CHAIR SEAT AND ITS CONTENTS. 